#+TITLE: Notes on “Babel: Introduction”
#+AUTHOR: Daniel
#+DATE: 2016-06-26

Tutorial from http://orgmode.org/worg/org-contrib/babel/intro.html

* Source Code Execution

#+begin_src hy
  (print "Hello, There!")
#+end_src

#+RESULTS:
: Hello, There!

#+begin_src sh
  echo "This file takes up `du -h emacs-org-babel-tutorial.org | sed 's/\([0-9k]*\)[ ]*emacs-org-babel-tutorial.org/\1/'`"
#+end_src

#+RESULTS:
: This file takes up 4.0K

#+begin_src R :colnames yes
  words <- tolower(scan("emacs-org-babel-tutorial.org", what="", na.strings=c("|",":")))
  t(sort(table(words[nchar(words) > 3]), decreasing=TRUE)[1:10])
#+end_src

#+RESULTS:
| #+begin_src | #+end_src | #+results: | date | plus | today's | :results | hello, | import | is") |
|-------------+-----------+------------+------+------+---------+----------+--------+--------+------|
|           5 |         5 |          4 |    3 |    3 |       3 |        2 |      2 |      2 |    2 |

** Capturing the Results of Code Evaluation

#+begin_src python :results value
  import time
  print("Hello, today's date is %s" % time.ctime())
  print("Two plus two is")
  return 2 + 2
#+end_src

#+RESULTS:
: 4

#+begin_src python :results output
  import time
  print("Hello, today's date is %s" % time.ctime())
  print("Two plus two is")
  2 + 2
#+end_src

#+RESULTS:
: Hello, today's date is Sun Jun 26 16:04:36 2016
: Two plus two is

** Session-based Evaluation

Have a look into /Emacs Speaks Statistics/

** Arguments to Code Blocks

#+name: square
#+header: :var x = 0
#+begin_src python
  return x*x
#+end_src

#+call: square(x=6)

#+RESULTS:
: 36

#+tblname: fibonacci-inputs
| 1 | 2 | 3 | 4 |  5 |  6 |  7 |  8 |  9 | 10 |
| 2 | 4 | 6 | 8 | 10 | 12 | 14 | 16 | 18 | 20 |

#+name: fibonacci-seq
#+begin_src emacs-lisp :var fib-inputs=fibonacci-inputs
  (defun fibonacci (n)
    (if (or (= n 0) (= n 1))
        n
      (+ (fibonacci (- n 1))
         (fibonacci (- n 2)))))

  (mapcar (lambda (row)
            (mapcar #'fibonacci row))
          fib-inputs)
#+end_src

#+RESULTS: fibonacci-seq
| 1 | 1 | 2 |  3 |  5 |   8 |  13 |  21 |   34 |   55 |
| 1 | 3 | 8 | 21 | 55 | 144 | 377 | 987 | 2584 | 6765 |

** In-line Code Blocks

In-line code can be call without header arguments (like so: src_sh{date}) or
with header arguments (like so: src_python[:results value]{return 10 + 10}).

** Code Block Body Expansion

Preview: =C-c C-v v=, bound to =org-babel-expand-src-block=

#+tblname: data
| username | john-doe |
| password | abc123   |

#+begin_src emacs-lisp :var data=data
(setq my-special-username (first (first data)))
(setq my-special-password (first (second data)))
#+end_src

** A Meta-programming Language for Org-mode

#+name: directories
#+begin_src sh :results replace
  cd ~ && du -sc * | grep -v total
#+end_src

#+RESULTS: directories
|   538604 | Desktop   |
| 77332656 | Documents |
|  1206668 | Mail      |
|        8 | News      |

#+name: directory-pie-chart
#+begin_src R :session R-pie-example :var dirs=directories
  pie(dirs[,1], labels = dirs[,2])
#+end_src

#+RESULTS: directory-pie-chart

Note: the syntax =#+name: directory-pie-chart(dirs=directories)= did not work.

** Using Code Blocks in Org Tables

*** Example 1: Data Summaries Using R

#+name: tbl-example-data
#+begin_src R
  runif(n=5, min=0, max=1)
#+end_src

#+name: R-mean
#+begin_src R :var x=""
  colMeans(x)
#+end_src

#+tblname: summaries
|              mean |
|-------------------|
| 0.574235895462334 |
#+TBLFM: @2$1='(org-sbe "R-mean" (x "tbl-example-data()"))

*** Example 2: Babel Test Suite

/No notes/

* The Library of Babel

#+lob: square(x=6)

Does not do what I expected …

* Literate Programming

#+name: hello-world-prefix
#+begin_src sh :exports none
  echo "/-----------------------------------------------------------\\"
#+end_src

#+name: hello-world-postfix
#+begin_src sh :exports none
  echo "\-----------------------------------------------------------/"
#+end_src

#+name: hello-world
#+begin_src sh :tangle hello.sh :exports none :noweb yes
  <<hello-world-prefix>>
  echo "|                       hello world                         |"
  <<hello-world-postfix>>
#+end_src

Tangling with =C-c C-v t=.

* Reproducible Research